1. Field of the Invention
The invention relates to a fuel property determination system for an internal combustion engine.
2. Description of the Related Art
An existing technique for determining the property of fuel used in an internal combustion engine is, for example, described in Japanese Patent Application Publication No. 2004-340026 (JP-A-2004-340026), Japanese Patent Application Publication No. 2009-68406 (JP-A-2009-68406) and Japanese Patent Application Publication No. 2004-308440 (JP-A-2004-308440). For example, JP-A-2004-340026 describes a control method for a compression ignition diesel engine. In the above existing control method, in a predetermined operating condition, an engine exciting force caused by an in-cylinder pressure is detected by exciting force detecting means that has a piezoelectric element. Then, the cetane number corresponding to the detected exciting force is determined on the basis of correlation data between an exciting force and a cetane number. The correlation data are created under the same operating condition in advance.
Combustion in a compression ignition internal combustion engine is significantly influenced by not only the cetane number determined in the above described existing control method but also an evaporation index, such as the distillation property of fuel. Thus, it is desirable to determine both the cetane number and the evaporation index at the same time. However, the above existing method is not able to determine the evaporation index together with the cetane number at the same time. In addition, in the case of a spark ignition internal combustion engine as well, similarly, it is desirably able to determine both the octane number and the evaporation index at the same time.